The present invention relates to switch housings, and particularly to switch housings for use in physical security alarm systems, for mounting sensor switches removably yet securely and unobtrusively in cavities such as holes bored in doorway frames.
When installing magnetic reed switches as parts of an intrusion detection system, it is typical to mount such switches for monitoring door closure in a position flush with a doorway casing by gluing a small cylindrical switch housing in place extending upward into a cavity defined in the horizontal top member of a doorway casing. A corresponding hole is drilled downward into the top of the door and the actuating magnet for the reed switch is mounted therein. Since removal of the switch for testing or replacement is occasionally desirable, gluing a switch housing into a cavity is disadvantageous. Nevertheless the switch housing needs to be held securely in place, or it might be loosened by normal vibration, allowing it eventually to slip down and interfere with the door, resulting in the switch being broken.
Small, protruding, wedge-like, longitudinal fins have been included on the outside of cylindrical switch housings to retain them in position, but are not completely satisfactory for retaining a housing in an overhead cavity without adhesives.
U.S. Pat. No. 3,560,690 to Luce et al. discloses a plunger switch for use in the doorways of automobiles. The switch includes deformable radially outwardly protruding louvers to provide a compression fit of the plunger switch into a bored hole in a doorway frame, but such a switch does not present the neat appearance and unobtrusiveness desired for a security alarm switch housing.
Wolfe, Jr. U.S. Pat. No. 4,700,163 discloses a housing for an alarm system sensor switch. A snap-in cap permits removal of the switch from the housing, but there is no provision for the housing itself to be self-retaining inside a cavity.
Chisholm et al. U.S. Pat. No. 4,728,238 and Wollar U.S. Pat. No. 4,396,329 both disclose fasteners for extending through holes in overlapping members to hold them together. Axially spaced-apart, radially extending flexible members fall generally within planes perpendicular to the length of the fastener and act to press together the members joined by the fasteners.
Hall et al. U.S. Pat. No. 3,177,540 discloses a panel fastener also useful for interconnecting overlapping members which define aligned bores. The Hall fastener includes radial fins which extend longitudinally along the length of the fastener and are flexible about the central axis of the fastener. The fins are tapered to facilitate insertion and thereafter to adjust themselves to proper holding of the members joined by the fastener.
Hauk U.S. Pat. No. 4,638,276 discloses a reed switch housing including exterior threads used to mount a reed switch precisely in machinery.
It has also previously been known to secure security alarm switch housings by screwing a threaded metal housing into a bored hole. Switch housings of this prior art design, however, require holes of relatively exact size and uniform bore, and are undesirably difficult to install. Such housings may be difficult to install where holes are incorrectly drilled or where adjacent layers of material defining a hole have become misaligned.
What is still needed, then, is a housing for use in unobtrusively and securely mounting small items such as security alarm system reed switch assemblies in easily formed cavities, as in finish woodwork or framing around doorways, and which permits easily withdrawal and subsequent reliably secure and easy replacement of the housing in such a cavity without use of an adhesive, despite a poorly shaped cavity or shifting of separate layers of materials after formation of a cavity.